1. Field of the Invention
The present invention relates to a cleaning apparatus and an image forming apparatus.
2. Description of the Related Art
As a cleaning apparatus employed in an image forming apparatus such as a copy machine, a facsimile, and a printer, a blade cleaning technique that presses a cleaning blade against a circumferential surface of an image carrier as a cleaning target to scrape and remove a toner on the image carrier has been known. The blade cleaning technique is widely being used thanks to a simple structure and a stable performance.
In recent years, there has been an increasing demand for improvement in image quality. As a result, particles of a toner become more spherical and smaller in diameter to satisfy such demand. The smaller diameter can improve the accuracy, definition, and resolution of an image. On the other hand, the more spherical shape improves a development property and a transfer property of a toner. However, it is difficult to perform effective cleaning on the spherical toner having the small particle diameter through the general cleaning blade technique. This is because of the following reasons. That is, a cleaning blade removes a toner by rubbing an image carrier surface with its edge part, but the edge part of the cleaning blade deforms due to the frictional resistance with the image carrier. Due to a so-called stick-slip phenomenon, a tiny void is formed between the image carrier and the cleaning blade. As the toner has a smaller diameter, the toner can more easily intrude into the void. Further, as the shape of the intruding toner is closer to the spherical shape, the toner may more easily rolls in the void due to generation of a rotational moment of the toner. For this reason, the spherical toner having the small diameter easily sneaks into the void between the cleaning blade and the image carrier.
In the case of using the spherical toner having the small particle diameter, a technique of preventing toner sneaking by increasing force (linear pressure) of the cleaning blade that comes in press contact with the image carrier may be considered. However, if pressing force increased and a high load is applied, the image carrier or the cleaning blade gets worn, and a lifespan extremely gets shorter. In recent years, an apparatus having a long lifespan is required, and thus a problem related to such durability should be avoided.
Meanwhile, as a technique of effectively cleaning the spherical toner having the small particle diameter, there is an electrostatic cleaning technique. This technique electrostatically removes the toner from the image carrier by applying a voltage of a polarity reverse to a charging polarity of the toner to a cleaning member such as a conductive cleaning blade that comes into contact with the image carrier.
However, the toner may not be completely removed through the electrostatic cleaning technique. This is because the charging quantity of the residual transfer toner that arrives as the cleaning member is variable as will be described later. Most part of the toner on the image carrier before a transfer is charged to the normal charging polarity of the toner (a negative polarity in this description). In a transfer unit, the toner on the image carrier is transferred to a transferred body when receiving a transfer electric field having a polarity (a positive polarity) reverse to the normal charging polarity of the toner. However, the toner may adhere to the image carrier “as is” as the residual transfer toner. Charges having the positive polarity applied by the transfer unit are injected into the residual transfer toner, so that the charge quantity shifts toward the positive polarity. For this reason, the residual transfer toner on the image carrier has a broad charge distribution in which the toner having the positive polarity and the toner having the negative polarity are mixed. In the electrostatic cleaning technique, since cleaning is electrostatically performed when a voltage having a polarity reverse to the normal charging polarity of the toner is applied to the cleaning member, it is difficult to collect the toner shifted to the positive polarity.
Japanese Patent Application Laid-open No. 2002-202702 discloses a cleaning apparatus in which a conductive blade that comes into contact with the image carrier and receives a voltage having a polarity reverse to a cleaning brush is disposed as a polarity control means for adjusting the charging polarity of the toner at an upstream side of a cleaning brush that is a cleaning member. According to the cleaning apparatus disclosed in Japanese Patent Application Laid-open No. 2002-202702, the residual transfer toner receives charges injected from the conductive blade when it passes through a position at which the conductive blade abuts on the image carrier (a blade abutting position), so that the charging polarity of the toner is adjusted to the same polarity (typically, the normal charging polarity of the toner) as the conductive blade. As a result, the charging polarity of the toner, which has arrived at a position where the cleaning blade comes into contact with the image carrier (a roller contact position) after passing through the blade abutting position, is adjusted to any one polarity (the same polarity as the conductive blade). Thus, right after the transfer, even the toner charged to the polarity reverse to the corresponding polarity can be electrostatically collected by the cleaning blade.
Further, Japanese Patent Application Laid-open No. 2007-25173 discloses a cleaning apparatus having a first cleaning brush to which a voltage of the polarity (the positive polarity) reverse to the normal charging polarity of the toner is applied and a second cleaning brush to which a voltage of the same polarity as the normal charging polarity of the toner is applied and which is disposed at a downstream side of the first cleaning brush. According to the cleaning apparatus disclosed in Japanese Patent Application Laid-open No. 2007-25173, the toner having the normal charging polarity (the negative polarity) on the image carrier is electrostatically absorbed onto the first cleaning brush serving as a normally-charged toner cleaning member and removed from the image carrier. The toner having the polarity (the positive polarity) reverse to the normal charging polarity on the image carrier is electrostatically absorbed onto the second cleaning brush serving as a revere charged toner cleaning member and removed from the image carrier. As a result, the toner inclined toward the positive polarity and the negative polarity toner can be removed from the image carrier.
When a toner pattern is formed on the image carrier by the control for adjusting image density and/or for correcting a misalignment in color superposition of an image, the density is read by a photo sensor, and an image creation condition is controlled based on the detection result, the toner pattern that was read is not transferred to a transfer sheet but removed by the cleaning apparatus. Even in a mode of consuming the toner to refresh the toner inside the developer or even when a jam occurs due to a transportation failure of paper, the created toner image is not transferred to the transfer sheet but removed by the cleaning apparatus. As described above, the cleaning apparatus also removes a non-transferred toner image that is a large amount of toner adhering to the image carrier, for example, the toner pattern as well as the residual transfer toner.
In the cleaning apparatus disclosed in Japanese Patent Application Laid-open No. 2002-202702, there are occasions that all particles in a large amount of toner that forms the non-transferred toner image cannot be adjusted to any one polarity by the polarity control means and thus the toner having the same polarity as the polarity applied to the cleaning brush enters the roller contact position. Further, there are also different occasions that it is difficult to electrostatically absorb a large amount of toner that forms the non-transferred toner to the brush of the cleaning brush. Therefore, in the cleaning apparatus disclosed in Japanese Patent Application Laid-open No. 2002-202702, if the non-transferred toner that is a large amount of toner adhering to the image carrier is input, cleaning failure may occur.
In the cleaning apparatus disclosed in Japanese Patent Application Laid-open No. 2007-25173, the first cleaning brush has the large diameter, and the second cleaning brush has the small diameter. By increasing the diameter size of the first cleaning brush, the nip width of the first cleaning brush increases, and a time in which the bristle contacts the image carrier increases. Further, since the length of the bristle increases, the contact area between the bristle and the toner increases. As a result, the amount of the toner that can be electrostatically absorbed by the first cleaning brush increases. Accordingly, a large amount of toner having the normal charging polarity can be removed by the first cleaning brush. Since most part of a toner that forms the non-transferred toner image to be input to the cleaning apparatus has the normal charging polarity, a large amount of non-transferred toner can be removed by the first cleaning brush when the non-transferred toner image is input.
Through the second cleaning brush having the small diameter to which a voltage of the same polarity as the normal charging polarity of the toner is applied, the toner having the normal charging polarity remaining on the image carrier that could not be removed by the first cleaning brush is mechanically removed, and the toner having the polarity reverse to the normal charging polarity is removed mechanically and electrostatically. If the second cleaning brush has the small diameter, the capability of electrostatically removing the toner of the polarity reverse to the normal charging capacity gets deteriorated. However, since the length of the bristle is short, the mechanical removing capability is improved. For this reason, the toner having the normal charging polarity remaining on the image carrier that could not be removed by the first cleaning brush can be mechanically effectively removed by the second cleaning brush. Since a small amount of the toner having the polarity reverse to the normal charging polarity is present in the non-transferred toner image, even though the capability of electrostatically removing the toner of the polarity reverse to the normal charging polarity of the second cleaning brush gets deteriorated, the toner having the polarity reverse to the normal charging polarity that passed through the first cleaning brush can be removed electrostatically and effectively by the second cleaning brush. Further, since the mechanical removing capability improves, mechanically removing is also enabled. Therefore, even though the capability of electrostatically moving the toner of the polarity reverse to the normal charging polarity of the second cleaning brush gets deteriorated, the toner having the polarity reverse to the normal charging polarity can be effectively removed by the second cleaning brush. In this way, the cleaning apparatus disclosed in Japanese Patent Application Laid-open No. 2007-25173 can prevent cleaning failure when the non-transferred toner that is a large amount of toner adhering to the image carrier is input.
However, in the cleaning apparatus disclosed in Japanese Patent Application Laid-open No. 2007-25173, electrostatic force of a repulsive direction acts on the toner charged to the normal charging polarity in the second cleaning brush to which a voltage having the same polarity as the normal charging polarity of the toner is applied. For this reason, even though the mechanical removing capability of the second cleaning brush increases, the toner having the normal charging polarity may pass through between the bristles without abutting on the bristles of the second cleaning brush. Thus, the sufficient mechanical capability is not obtained, resulting in the cleaning failure. Further, when removing the residual transfer toner, there are occasions that a large amount of the toner having the polarity reverse to the normal charging polarity is present. In such occasions, the residual toner having the polarity reverse to the normal charging polarity may not be effectively removed by the second cleaning brush in which the capability of electrostatically absorbing and removing the toner gets deteriorated due to the small particle diameter. This results in the cleaning failure.